linux-kernel - Re: [PATCH] powerpc: Fix missing declaration of [en/dis]able_kernel

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Date:   Tue, 9 Mar 2021 09:45:20 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        Christian König <christian.koenig@....com>,
        Alex Deucher <alexdeucher@...il.com>
Subject: Re: [PATCH] powerpc: Fix missing declaration of [en/dis]able_kernel_vsx()

Hi Christophe,

On Tue, Mar 9, 2021 at 9:39 AM Christophe Leroy
<christophe.leroy@...roup.eu> wrote:
> Add stub instances of enable_kernel_vsx() and disable_kernel_vsx()
> when CONFIG_VSX is not set, to avoid following build failure.
>
>   CC [M]  drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dcn_calcs.o
> In file included from ./drivers/gpu/drm/amd/amdgpu/../display/dc/dm_services_types.h:29,
>                  from ./drivers/gpu/drm/amd/amdgpu/../display/dc/dm_services.h:37,
>                  from drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dcn_calcs.c:27:
> drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dcn_calcs.c: In function 'dcn_bw_apply_registry_override':
> ./drivers/gpu/drm/amd/amdgpu/../display/dc/os_types.h:64:3: error: implicit declaration of function 'enable_kernel_vsx'; did you mean 'enable_kernel_fp'? [-Werror=implicit-function-declaration]
>    64 |   enable_kernel_vsx(); \
>       |   ^~~~~~~~~~~~~~~~~
> drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dcn_calcs.c:640:2: note: in expansion of macro 'DC_FP_START'
>   640 |  DC_FP_START();
>       |  ^~~~~~~~~~~
> ./drivers/gpu/drm/amd/amdgpu/../display/dc/os_types.h:75:3: error: implicit declaration of function 'disable_kernel_vsx'; did you mean 'disable_kernel_fp'? [-Werror=implicit-function-declaration]
>    75 |   disable_kernel_vsx(); \
>       |   ^~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dcn_calcs.c:676:2: note: in expansion of macro 'DC_FP_END'
>   676 |  DC_FP_END();
>       |  ^~~~~~~~~
> cc1: some warnings being treated as errors
> make[5]: *** [drivers/gpu/drm/amd/amdgpu/../display/dc/calcs/dcn_calcs.o] Error 1
>
> Fixes: 16a9dea110a6 ("amdgpu: Enable initial DCN support on POWER")
> Cc: stable@...r.kernel.org
> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>

Thanks for your patch!

> --- a/arch/powerpc/include/asm/switch_to.h
> +++ b/arch/powerpc/include/asm/switch_to.h
> @@ -71,6 +71,16 @@ static inline void disable_kernel_vsx(void)
>  {
>         msr_check_and_clear(MSR_FP|MSR_VEC|MSR_VSX);
>  }
> +#else
> +static inline void enable_kernel_vsx(void)
> +{
> +       BUILD_BUG();
> +}
> +
> +static inline void disable_kernel_vsx(void)
> +{
> +       BUILD_BUG();
> +}
>  #endif

I'm wondering how this is any better than the current situation: using
BUILD_BUG() will still cause a build failure?

What about adding "depends on !POWERPC || VSX" instead, to prevent
the issue from happening in the first place?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds